1. Field of the Invention
The present invention relates to a laser dicing device and a dicing method for dividing a wafer on which semiconductor devices, electronic components, or the like are formed, into respective chips.
2. Description of the Related Art
Conventionally, to divide a wafer, in which semiconductor devices, electronic components, or the like are formed on the surface, into respective chips, a dicing device has been used to form ground grooves in the wafer by a thin grindstone of about 30 μm thick made of small diamond abrasive grains, and cut the wafer.
In a dicing device, a thin grindstone (hereinafter referred to as a dicing blade) is rotated at a high speed of about 30,000 to 60,000 rpm to grind a wafer to thereby completely cut (full-cut) or incompletely cut (half-cut or semi-full cut) the wafer.
However, in the case of a grinding work performed by such a dicing blade, as a wafer is a high brittle material, processing is performed in a brittle mode. As such, chipping occurs on the surface and the rear face of the wafer. This chipping causes degradation in the performance of the divided chips. Particularly, the chipping occurred on the rear face has been a big problem because it causes cracks to gradually advance toward the inside the wafer.
To address such a problem, a laser dicing device has been proposed, in which a laser light is emitted with the condensing point focused inside a wafer to form a modified region inside the wafer by multiphoton absorption to thereby divide the wafer into respective chips, instead of conventional cutting by a dicing blade (see Japanese Patent Application Laid-Open No. 2007-167918, for example. hereinafter referred to as PTL 1). In such a laser dicing device, it is necessary to control the position of the condensing point of the laser light with high accuracy by detecting the position of the surface (height) of the wafer with use of an autofocus mechanism in order to form the modified region to be formed inside the wafer at a certain depth from the surface of the wafer.
For example, in the technology disclosed in PTL 1, a processing laser light for forming a modified region and an AF (for ranging) laser light for detecting the position of the surface of the wafer are condensed toward the wafer on a light path shared by the lasers by a condenser lens. At this time, the reflected light of the AF laser light reflected by the surface of the wafer is detected, and according to the detected signal, the position of the condenser lens is finely adjusted in a wafer thickness direction so as to allow the position of the condensing point of the processing laser light to be located at a position having a certain distance from the surface of the wafer. Thereby, it is possible to perform real time processing to form the modified region at a desired position inside the wafer, while controlling the position of the condensing point of the processing laser light so as to follow a displacement of the surface of the wafer.